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In this study, a facile method for the synthesis of leach proof and earth-abundant non-noble Ni nanoparticles on N-doped carbon nanotubes is reported. The catalyst was synthesized by an impregnation-carbonization method, wherein a Ni-chitosan complex upon carbonization in a 5% H2/N2 atmosphere at 800 °C yielded Ni-containing N-doped CNTs. Chitosan served as a single source of carbon and nitrogen, and the nanotube growth was facilitated by the in situ formed Ni nanoparticles. The nanocatalyst was thoroughly characterized by several techniques; elemental mapping by SEM and TEM analysis confirmed the uniform distribution of Ni nanoparticles on the surface of N-doped CNTs with an average size in the range of 10-15 nm. The catalyst efficiently reduced a variety of nitroarenes (>99%) into their corresponding amines at a moderate pressure (5 bar) and a comparatively lower temperature (80 °C). Furthermore, the easy recovery of the catalyst using an external magnetic field along with high activity and easy recyclability makes the protocol eco-friendly.

We report a solution-phase synthetic route to copper nanoparticles with controllable size and shape. The synthesis of the nanoparticles is achieved by the reduction of copper(II) salt in aqueous solution with hydrazine under air atmosphere in the presence of poly(acrylic acid) (PAA) as capping agent. The results suggest that the pH plays a key role for the formation of pure copper nanoparticles, whereas the concentration of PAA is important for controlling the size and geometric shape of the nanoparticles. The average size of the copper nanoparticles can be varied from 30 to 80 nm, depending on the concentration of PAA. With a moderate amount of PAA, faceted crystalline copper nanoparticles are obtained. The as-synthesized copper nanoparticles appear red in color and are stable for weeks, as confirmed by UV/Vis and X-ray photoemission (XPS) spectroscopy. The faceted crystalline copper nanoparticles serve as an effective catalyst for N-arylation of heterocycles, such as the C--N coupling reaction between p-nitrobenzyl chloride and morpholine producing 4-(4-nitrophenyl)morpholine in an excellent yield under mild reaction conditions. Furthermore, the nanoparticles are proven to be versatile as they also effectively catalyze the three-component, one-pot Mannich reaction between p-substituted benzaldehyde, aniline, and acetophenone affording a 100% conversion of the limiting reactant (aniline).